Advances in Ion-Beam-Driven High Energy Density Physics and Heavy Ion Fusion

1. Recent advances in ion-beam-driven high energy density physics and heavy ion fusion* Presented by Ronald C. Davidson on behalf of the Heavy Ion Fusion Science Virtual National Laboratory** Presented at 2006 Fusion Power Associates Symposium Washington, D.C. 20003 September 27 - 28, 2006 *This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Berkeley and Lawrence Livermore National Laboratories under Contract Numbers DE-AC02-05CH1123 and W-7405-Eng-48, and by the Princeton Plasma Physics Laboratory under Contract Number DE-AC02-76CH03073. ** HIFS-VNL: A collaboration between Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, and Princeton Plasma Physics Laboratory, USA.

2. Outline • Program objectives • Neutralized drift compression • Design of ion-beam-driven warm dense matter target experiments • Pulse-Line Ion Accelerator (PLIA) • High brightness beam transport • Advanced theory and simulation tools • Studies of neutralized drift compression applied to heavy ion fusion drivers • Conclusions

3. Program objectives Top-level scientific question fundamental to both high energy density physics and heavy ion fusion: “How can heavy ion beams be compressed to the high intensities required for creating high energy density matter and fusion?” Goals: Understand the beam and plasma target science to enable: • An upgrade to the present Neutralized Drift Compression Experiment (NDCX). • An integrated beam user facility Integrated Beam-High Energy Density Physics Experiment (IB-HEDPX). Advances in the past two years will enable first heavy ion beam-target interaction experiments to begin in 2008.

4. The r - T regime accessible by beam-driven experiments is similar to the interiors of giant planets and low-mass stars Figure adapted from “Frontiers in HEDP: the X-Games of Contemporary Science:” Accessible region using Intense beams Region is part of Warm Dense Matter (WDM) regime WDM lies at crossroads of: degenerate /classical and strongly Coupled/ weakly coupled Terrestial planet

5. We are pursuing a unique approach to ion-beam-driven warm dense matter physics using short range ions Ion energy loss rate in targets dE/dx Maximum dE/dx and uniform heating at this peak require short (~ 1 ns) pulses to minimize hydro motion. [L. Grisham, Phys. Plas. 11, 5727 (2004)] Te > 10 eV @ 20J, 20 MeV (Future US accelerator for HEDP/fusion) 30 mm 0.1x solid z 3 mm GSI: 40-100 GeV heavy Ions thick targets Te ~ 1 eV per kJ Dense, strongly coupled plasmas @ 10-2 to 10-1x solid density are potentially interesting areas to test EOS models (Numbers are % disagreement in EOS models where there is little or no data) (Courtesy of Richard Lee, LLNL)

6. New theoretical EOS work meshes very well with the experimental capabilities we will be creating Large uncertainties in WDM region arise in the two phase (liquid-vapor) region. Accurate results in two-phase regime essential for WDM. Richard More has recently developed new high-quality EOS for Sn. Interesting behavior in the T~1.0 eV regime. Richard Lee plot of contours of fractional pressure difference for two common EOS P (J/cm3) Critical point unknown for many metals, such as Sn r (g/cm3) T (eV) EOS tools for this temperature and density range are just now being developed.

7. Longitudinal bunch compression in the Neutralized Drift Compression Experiment (NDCX)*: pulses now short enough to begin target experiments Induction core impresses head-to-tail velocity ramp (“tilt”) on 200-ns slices of injected 300 keV K+ ion beam, compressing the slices to few nanoseconds. Induction waveform End beam current with/ without velocity ramps Same injector as the previous NTX experiment Longer plasma source ~1 m * P.K. Roy et al., Phys. Rev. Lett. 95, 234801 (2005).

8. Simulations of neutralized beam compression (red curve) are in very good agreement with the NDCX data (black curve) when experimental induction waveforms are used in the simulations. 4.5 ns FWHM

9. Transverse focusing in background plasma has been demonstrated in the Neutralized Transport Experiment Measurements on the Neutralized Transport Experiment (NTX) demonstrate achievement of smaller transverse spot size using volumetric plasma. Neither plasma plug nor volumetric plasma. Plasma plug. Plasma plug and volumetric plasma.

10. LSP PIC simulations: Optimizing approach to 2008 WDM experiments Proposed improved tilt core waveform (Simulationsby Adam Sefkow, PPPL )

11. We are preparing for a sequence of WDM experiments, beginning at low beam intensities and target temperatures time We are also discussing near-term collaborative experiments with GSI, Sandia, and other laboratories.

12. Near term plans: NDCX experimental target chamber is under construction, and diagnostics are being developed The Heavy Ion Fusion Science Virtual National Laboratory 12

13. Evaluating the feasibility of a new Pulse-Line Ion Accelerator (PLIA) (Concept proposed by R.J. Briggs) (a) The helical pulse line of radius r is located inside a conducting cylinder of radius b, and a dielectric medium is located in the region outside the helix; (b) schematic of a drive voltage waveform applied at the helix input; and (c) a one-meter-long helix constructed for the PLIA experiments.

14. First PLIA test validates acceleration principle The measured ion output energies (a) are modulated depending on the ion phase with respect to the ringing waveform. WARP-3D simulations (b) reproduce the measured energy modulation (P.K. Roy, E. Henestroza, J. Coleman, A. Friedman et al).

15. High Current Experiment (HCX) benchmarks models for unique modeling capability for electron cloud and gas effects (a) (b) (c) Simulation Experiment 0V 0V 0V/+9kV 0V Four HCX magnetic quadrupoles e- 200mA K+ Q1 Q2 Q3 Q4 WARP-3D T = 4.65s Electrons Electron and gas cloud modeling critical to all high current accelerators, including high energy physics: LHC, ILC, …and future HEDP/fusion drivers: NDCX-II, IB-HEDPX . 200mA K+ Slope ~1 mm/µs Beam ions hit end plate Electrons bunching Oscillations 0. -20. -40. 6 MHz oscillations in (C) in simulation AND experiment I (mA) (c) 0. 2. time (s) 6.

16. Strong Harris Instability for Beams with Large Temperature Anisotropy(This may limit minimum Tpar<Tperp longitudinal compression)* • Moderate intensity  largest threshold temperature anisotropy. • BEST simulations show nonlinear saturation by particle trapping  tail formation. • E. A. Startsev, H. Qin and R. C. Davidson, Physical Review Special Topics on • Accelerators and Beams 8, 124201 (2005).

17. 0.1 solid Al 0.01 solid Al (at t=2 ns) Hydra simulations confirm temperature uniformity of targets at 0.1 and 0.01 times solid density of aluminum (20 MeV Ne+) 0 Dz = 48 m r =1 mm 0.7 1.0 Axis of symmetry 1.2 2.0 t(ns) 2.2 Dz = 480 m

18. To validate IB-HEDPX (heavy-ion HEDP user facility) we plan a modest increment to upgrade NDCX-I NDCX-II Neutralized Compression Final Focus Solenoid Focusing Helix Acceleration Short Pulse Injector 1 eV target heating >0.1 mC of Na+ @ 24 MeV heating @ Bragg peak dE/dx NDCX-1C + $5M hardware Concept above uses a PLIA for 24 MeV Na+, assuming gradient improves. Alternative: 2.8 MeV Li+ using induction.

19. Outlook for next 10 years Challenge 1: (NDCX-I) Understand limits to compression of neutralized beams. Excellent progress (>50X longitudinal; > 200 transverse). Opportunities for many improvements Challenge 3: Ion-HEDP user facility DOE Mission Need 12-1-05. CD-1 requires NDCX-II pre-requisite. May prototype approach to HIF Challenge 2: Integrated compression, acceleration and focusing sufficient to reach 1 eV in targets: Assessing backup induction approach with 2.8 MeV Lithium. Add acceleration (either PLIA or induction-TBD) Add chambers, targets, HEDP diagnostics

20. The National Task Force report on HEDP summarizes the ten-year plan for heavy ion beam science. HIF target and chamber science are missing. Fig 3.1 , page 33, 2004 National Task Force report

21. At the budget levels identified in the National Task Force report, we would continue to pursue WDM physics on NDCX as well as opportunities for additional driver, chamber and target science 1. We can complete the knowledge base needed to evaluate both quadrupole as well as solenoid-based drivers for HEDP and HIF: - First data on e-cloud effects with heavy ion beams in solenoids. - HCX could test halo scrapers and induction gaps to mitigate e-clouds in magnetic quadrupoles (at modest incremental cost) - Resume negative ion source research 2. Optical drive solid state switching + fast kickers (LLNL Beam Research innovations) may enable linac multi-pulsing and time-dependent corrections for compression velocity tilts improved target pulse shaping capability with fewer beams for both HEDP and HIF (can test on NDCX). 3. Compact liquid vortex chambers with embedded magnetic field may allow higher pulse rates and shorter focal lengths  smaller focal spot size. (Can use existing UC Berkeley laboratory equipment.) 4. Advanced HIF target design plus NIF and Z data may lead to lower heavy ion fusion driver requirements.

22. Work in progress: we are evaluating ways to apply what we learn from our HEDP research towards heavy ion fusion energy Sketch of a modular, multi-pulse heavy ion driver. Pulses overlap at the target 500 TW peak power in 2 ns Key enabling advances that will help both HEDP and fusion: Neutralized drift compression and focusing. Time-dependent correction for improved achromatic focusing. Multi-pulse longitudinal merging and pulse shaping. Fast agile optically-driven solid state switching.

23. NIF ignition can validate hohlraum x-ray transport and capsule physics relevant to indirect drive approaches like heavy ion fusion

24. Conclusions • There have been many exciting scientific advances and discoveries during the past year that enable: - Demonstration of compression and focusing of ultra-short ion pulses in neutralizing plasma background. - Unique contributions to High Energy Density Physics and Heavy Ion Fusion - Contributions to cross-cutting areas of accelerator physics and technology, e.g., electron cloud effects, diagnostics, advanced simulation techniques, beam interaction targets. • Heavy ion research on neutralized drift compression and e-cloud effects is of fundamental importance to both HEDP in the near term and fusion in the longer term. • Experiments heavily leverage existing equipment and are modest in cost. • Theory and modeling play a key role in guiding and interpreting experiments. • There are new tools and knowledge to update studies of heavy ion fusion.

25. Back-up

26. Contributors to this research Lawrence Berkeley National Laboratory B. G. Logan, J. Armijo, D. Baca, F.M. Bieniosek, C.M. Celata, S. Chilton, J. Coleman, J. Correa, S. Eylon, W. Greenway, E. Henestroza, J.W. Kwan, E. P. Lee, C. Leister, M. Leitner, S. Perez, L. Reginato, P.K. Roy, P. Santhanam, P.A. Seidl, J-L. Vay, W.L. Waldron, S.S. Yu Lawrence Livermore National Laboratory J.J. Barnard, R.H. Cohen, A. Friedman, D.P. Grote, M. Kireeff Covo, A.W. Molvik, S.M. Lund, W.R. Meier, W. Sharp Princeton Plasma Physics Laboratory R.C. Davidson, P.C. Efthimion, E.P. Gilson, L. Grisham, I.D. Kaganovich, H. Qin, A.B. Sefkow, E.A. Startsev Voss Scientific D.R. Welch Sandia National LaboratoriesC. Olson SAICR.J. Briggs

27. Simulations show that solenoidal magnetic field influences neutralizing effects of background plasma Plots of electron charge density contours in (x,y) space, calculated in 2D slab geometry using the LSP code with parameters: Plasma: np=1011cm-3; Beam: Vb=0.2c, 48.0A, rb=2.85cm and pulse duration b=4.75 ns. A solenoidal magnetic field of 1014 G corresponds to ce=pe. • In the presence of a solenoidal magnetic field, whistler waves are excited, which propagate at an angle with the beam velocity and can perturb the plasma ahead of the beam pulse.

28. Proof-of-concept experiments demonstrate feasibility of negative halogen ions Cl (electron affinity 3.61 eV) yields far more negative ions and far fewer electrons than O (1.46 eV affinity), confirming that greater electron affinity allows closer approach to ion-ion extractor plasma • Negative ions offer potential advantages over positive ions for heavy ion fusion: • Will not draw electrons from surfaces. • Charge exchange tails much less than for positive ions from plasma source (helps longitudinal emittance). • If atomic beams desired, can be efficiently converted to neutrals by photodetachment. • Initially atomic driver beams could reduce average beam self-perveance and target spot size even if ionized en route to the target. • Experiments indicate surprisingly low effective ion temperatures for both Cl- and Cl+; if confirmed by more measurements, ions from ion-ion plasmas may offer lower emittance than from electron-ion plasmas.

29. The Heavy Ion Fusion Virtual National Laboratory PLIA can be operated in the short pulse (“surfing”) mode or the long pulse (“snowplow”) mode Short beam “surfs” on traveling voltage pulse (snapshots in wave frame) V (kV) Ex/10 (kV) z(m) z(m) z(m) z(m) z(m) z(m) z(m) z(m) z(m) z(m) Longer beam is accelerated by “snowplow” (snapshots in lab frame) V (kV) Ex (kV) z(m) z(m) z(m) z(m) z(m)

30. 7.5 x(mm) -7.5 0.5 1.0 0. 1.5 z (m) Merging beamlet injector experiments on STS-500 validated the concept of this compact, high current source • Monolithic solid sources suffer from poor scaling versus size at high currents. • This new concept circumvents the problem via use of many small, low-current source. Simulation Experiment From a full-gradient (parallel-beamlet) experiment y (m) -0.05 x (m) 0.05 -0.05 x (m) 0.05 • From scaled merging experiment: • Obtained emittances comparable to simulation. • Effects of “dirty” physics (electrons, charge exchange) were minimal. • Scales to 0.5 A, 1.6 MeV, ~1 -mm-mrad, 13 mA/cm2

31. In-bore diag. K+ beam Intercepting diagnostics Intercepting diagnostics Also e- coeff.; gas desorption coeff. (GESD) Suppressor Clearing electrodes The High Current Experiment (HCX) is exploring beam transport limits Focus of Gas/Electron Experiments K+ Beam Parameters I = 0.2 (- 0.5) Amp 1 (- 1.7) MeV, 4.5 ms 2 MV INJECTOR MATCHING SECTION ELECTROSTATIC QUADRUPOLES MAGNETIC QUADRUPOLES 4 magnetic quadrupoles; many diagnostics

32. (b) (c) (a) e- Suppressor on Suppressor off 0V 0V 0V V=-10kV, 0V experiment simulation Comparison: Clearing electrodes and e-suppressor on/off e-supp 200mA K+ • Beam ions • Electrons from ions hitting surface • Secondary electrons Comparison indicates semi-quantitative agreement.

33. Initial solenoid transport experiment in NDCX using a 25 mA, 300 keV K+ ion beam through two 3T solenoids Two-solenoid NDCX Transport Experiment Diagnostics and modeling are being carried out to understand transport, including e-cloud and gas effects in four solenoids (P. Seidl, A. Molvik et al). We are comparing transport of high perveance beams in solenoids and quadrupoles. Beam Image WARP PIC Model

34. We have almost completed the implementations of all of the modules needed for self-consistent modeling of electron and gas cloud effects in high intensity ion accelerators*. *(Cohen, J. Luc Vay et al) Implemented modules are in red; those undergoing implementation are in blue.

35. NIF and Z results on hohlraum and capsule physics can be relevant to a broad range of heavy ion fusion target options Some features of HIF target designs might improve NIF and Z targets: e.g., close-coupled hohlraums, shine shields, p4 shims.